1. Field of the Invention
The present invention relates to techniques for reactively converting hydrocarbons. More particularly, the invention relates to systems and methods for reactive co-conversion of heavy hydrocarbon materials and hydrocarbon gases to lighter hydrocarbon materials.
2. Background Technology
Heavy hydrocarbon materials, such as heavy oil, include any petroleum/crude oil that has a low API (American Petroleum Institute) gravity of less than 20 API degrees or a high specific density of more than about 0.9 g/ml. Heavy oil is quite viscous, does not flow well and has a high carbon to hydrogen ratio along with a high amount of carbon residues due to coking process, asphaltenes, sulfur, nitrogen, and heavy metals. The importance of heavy oil is increasing as more supplies of light oil start to decrease and run out. Most of the world's remaining oil resources and reserves primarily contain heavy oil.
Generally, oil refineries are designed for handling lighter crude oils, which typically have a density of about 0.8 g/ml or less. Because heavy oils have a higher density, a high sulfur content, and are highly viscous (sometimes over 1000 times more viscous than light crude oil), they are less than ideal for conventional oil refineries. Therefore, in order to capitalize on heavy oils as a source for transportation fuel, present processes found in the art seek to upgrade heavy oils into a practical intermediate to sell and transport to refineries.
One of the goals of upgrading is to make the heavy oil capable of being transported by pipeline without adding a solvent. Currently, solvents are usually required which require an additional solvent-recovery process. The ultimate goal of upgrading is to make an economically valuable synthetic crude oil. However, this requires large, expensive plants, much like refineries. Further, current processes require multiple steps.
For example, one process of upgrading heavy oils uses a solvent to dilute the heavy oil, which is then distilled. Large molecules that will not distill out are thermally cracked at over 400° C to produce lighter hydrocarbons. Since the resulting product is rich in nitrogen and sulfur, a second thermal cracking step is required to reduce sulfur content. Thermal cracking requires hydrogen gas to stabilize the process. The hydrogen suppresses coke formation and helps remove sulfur.
The current state of the art for upgrading heavy oil can be divided into two general approaches: 1) hydrogen addition, and 2) carbon rejection. Hydrogen addition processes are often desirable because of high liquid yield. However, these types of processes are expensive, requiring high temperature and pressure equipment as well as a hydrogen source. Carbon rejection plants and processes are also desirable because they are less expensive to construct and operate. However, carbon rejection processes produce large quantities of very low-grade materials, which are not always readily marketable or disposable, and with heavy oils, have high yield losses.
Methane remains another vastly unused resource. Methane is an abundant hydrocarbon fuel and chemical feed stock, and is expected to remain so for quite some time. Yet, because of capital and technological barriers, methane has remained an under-utilized resource throughout the world.
Thus, it would be desirable to provide improved methods for upgrading heavy oils that avoid or overcome the difficulties and problems of prior techniques.